WO2001067444A1 - Recovery from tracking errors on optical disks - Google Patents

Recovery from tracking errors on optical disks Download PDF

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Publication number
WO2001067444A1
WO2001067444A1 PCT/KR2000/000611 KR0000611W WO0167444A1 WO 2001067444 A1 WO2001067444 A1 WO 2001067444A1 KR 0000611 W KR0000611 W KR 0000611W WO 0167444 A1 WO0167444 A1 WO 0167444A1
Authority
WO
WIPO (PCT)
Prior art keywords
servo
scratch
disc
error
particle
Prior art date
Application number
PCT/KR2000/000611
Other languages
French (fr)
Inventor
Young-San Ko
Original Assignee
Cns Co., Ltd.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Cns Co., Ltd. filed Critical Cns Co., Ltd.
Priority to AU2000251131A priority Critical patent/AU2000251131A1/en
Publication of WO2001067444A1 publication Critical patent/WO2001067444A1/en

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Classifications

    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
    • G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
    • G11B7/0946—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following specially adapted for operation during external perturbations not related to the carrier or servo beam, e.g. vibration
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B19/00—Driving, starting, stopping record carriers not specifically of filamentary or web form, or of supports therefor; Control thereof; Control of operating function ; Driving both disc and head
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
    • G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
    • G11B7/0941—Methods and circuits for servo gain or phase compensation during operation
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
    • G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
    • G11B7/0948—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following specially adapted for detection and avoidance or compensation of imperfections on the carrier, e.g. dust, scratches, dropouts

Definitions

  • the present invention relates to a servo apparatus in an optical disc system, and more particularly, to a servo apparatus for detecting a tracking error on an optical disc by using multi-laser beam etc.
  • An optical disc system such as a CD (Compact Disc), an LD (Laser Disc) and an MD (Mini Disc) etc. generally employs a digital storing method in storing data, and utilize non-contact reproducing method in playback of the stored data.
  • the non-contact reproducing method is accomplished by performing non-contact reproducing of bit signals written on a disc by using light such as laser beam etc. and executing a digital signal process on the reproduced bit signals. It has well known in the related field that the optical disc system provides an improvement of a performance and an operation in a random access or a program reproduction etc. based on non-contact reproduction, the improvement being hard to be realized in an analog storage/reproduction system.
  • Fig. 1 shows a schematic construction of an optical pick-up apparatus for reading data stored in a disc in an optical disc system.
  • digital information is recorded in a disc 11 along a track (not shown), and laser beam focused by an object lens is irradiated onto a signal face of the disc 1 1
  • a focusing actuator coil 13 drives the object lens 12 so that the signal face of the disc 11 is positioned at the focal point of the laser beam
  • a tracking actuator coil 14 drives the object lens 12 so that the laser beam using for an optical pick-up can be traced along by the track of the disc 11
  • a focusing servo is generally executed and a tracking servo is performed for the laser beam used for optical pick-up to be exactly traced along the track
  • Fig 2 indicates a circuit construction of a servo apparatus for detecting a conventional focusing error
  • a focusing error signal is provided to a phase compensating part 21 to compensate a phase thereof, and then, is sent to a dm ing part 22
  • the driving part 22 drives a focusing actuator coil 23 in response to the focusing error signal compensated in phase
  • the object lens 12 of the optical pick-up apparatus shown in Fig 1 is adjusted and the signal face of the disc 11 is positioned at the focal point of the laser beam
  • phase compensating part 21 is to adjust the amount of the variation of the object lens 12 corresponding to the focusing error signal through changing of the phase of the focusing error signal That is, the phase is delayed for a specific focusing error signal, the object lens 12 insensibly react thereto while, when the phase is advanced, the object lens 12 sensibly react thereto
  • the sensibility of the phase compensating part 21 is properly determined and set such that a reaction of the object lens 12 for the focusing error signal ma> be adequate
  • Fig 3 depicts a circuit construction of a servo apparatus for detecting a conventional tracking error.
  • a tracking error signal is transmitted to a phase compensating part to compensate a phase thereof, and then, the compensated signal is sent to a driving part.
  • the driving part drives a tracking actuator coil in response to the tracking error signal compensated in the phase. As the tracking actuator coil is driven, the object lens is traced to an eccentricity of the disc.
  • the purpose of the present invention is to provide a servo apparatus for detecting a tracking error in an optical disc system, which is capable of settling the above-mentioned problems.
  • Another purpose of the present invention is to provide a servo apparatus for detecting a tracking error in an optical disc system, in which an influence caused by a scratch or particle on the disc surface or a fine vibration by an external cause can be minimized.
  • the servo apparatus for detecting a tracking error in an optical disc system is characterized by: at least two servo error detecting parts for outputting a servo error signal to determine whether or not there is a scratch or a particle on the surface of the disc, or a vibration of the optical disc by an external cause: a comparing part for recognizing the magnitude of the servo signals generated from said at least two servo error detecting parts and generating a signal representative of whether or not there is a scratch or a particle on the surface of the optical disc, or an occurrence of the vibration of the optical disc by an external cause; and a controlling part for minimizing a system error caused by the scratch or the particle of the optical disc surface and the vibration in response to a signal outputted from the comparing part.
  • Fig. 1 shows a schematic structure diagram of an optical pick-up apparatus for reading data stored in a disc
  • Fig. 2 depicts a block diagram showing a servo apparatus for detecting a focusing error
  • Fig. 3 depicts a block diagram showing a ser ⁇ o apparatus for detecting a tracking error.
  • Fig. 4 depicts a block diagram showing a servo apparatus for detecting a tracking error in an optical disc system in accordance with the preferred embodiment of the present invention
  • Fig. 5 shows an output waveform diagram of the servo apparatus shown in Fig. 4, in the case of a scratch or particle on a disc surface.
  • Fig. 6 shows an output waveform diagram of the servo apparatus in Fig. 4, in the case of a vibration of a disc.
  • Fig. 4 shows a servo apparatus for detecting a tracking error in an optical disc system in the preferred embodiment of the invention.
  • each of error signals 1, 2 is measured by a first servo error detecting part 100 and a second error detecting part 102 using a laser beam etc. and the measured signals 1 , 2 are inputted to a comparing part 104.
  • the number of the servo detecting part for outputting error signals can be reduced or increased according to the number of the laser beam irradiated, and in the embodiment, the number of the servo detecting part is not limited to two, rather increased two or more.
  • the comparing part 104 measures the magnitude of the error signals 1 , 2 and sends a signal representative of an defect caused by a disc surface, i.e.. a scratch or particle on the disc surface, or the vibration of the disc, to a controlling part 106. That is. if the following condition is satisfied:
  • the signals 1 , 2 are inputted to the controlling part 106. and in the controlling part, it is recognized as a scratch or particle existing on the disc surface when both of the signals 1 , 2 are in active state, thereby a switch SW is cut off. In case only the signal 1 is in active, the switch is opened and the gain of a gain/compensating part 112 becomes large to make the servo apparatus have a strong characteristic against the vibration.
  • a delaying part 108 delays the error signal 1 so as not to have little influence upon the servo apparatus due to a scratch or particle.
  • Fig. 5 shows output waveform from the servo apparatus shown in Fig. 4, in the case of a scratch or particle existing on the disc surface
  • Fig. 6 depicts output waveform obtained in the case of a vibration.
  • the error signal 1 (waveform a) and the error signal 2(waveform b) are outputted from the first and second servo error detecting parts 100. 102 at a constant time interval. Then, the error signal 1 is delayed and outputted (waveform c) through the delaying part 108.
  • the switch is cut off to thus generate waveform d and a subtracting part 110 outputs waveform e.
  • the error signal 1 , 2(waveform a-1 and b-1 ) are outputted from the first and second servo error detecting parts 100. 102 at the same time.
  • a gain is increased to make the servo apparatus have a strong characteristic against the vibration as shown in waveform c-1.
  • the servo apparatus for detecting the tracking error comprises at least two servo error detecting parts for generating a servo error signal in order to determine whether there is a scratch or particle on the surface of the optical disc, or a vibration due to the external cause, in which the servo error detecting part uses a laser beam.
  • the servo error detecting part uses a laser beam.

Abstract

A servo apparatus for detecting a tracking error in an optical disc system comprises at least two servo error detecting parts for generating a servo error signal to determine whether there is a scratch or particle on the surface of an optical disc, or a vibration of the optical disc by any external cause. As a result, by determining whether it is a disregardabe scratch or particle on the disc surface and minimizing the possibility of errors in the servo apparatus, and in the case of a vibration of the disc by any external cause, by increasing a gain, a servo apparatus strong against a shock can be realized.

Description

RECOVERY FROM TRACKING ERRORS ON OPTICAL DISKS
BACKGROUND OF THE INVENTION Field of the invention
The present invention relates to a servo apparatus in an optical disc system, and more particularly, to a servo apparatus for detecting a tracking error on an optical disc by using multi-laser beam etc.
Discussion of the Related Art
An optical disc system such as a CD (Compact Disc), an LD (Laser Disc) and an MD (Mini Disc) etc. generally employs a digital storing method in storing data, and utilize non-contact reproducing method in playback of the stored data. Generally, the non-contact reproducing method is accomplished by performing non-contact reproducing of bit signals written on a disc by using light such as laser beam etc. and executing a digital signal process on the reproduced bit signals. It has well known in the related field that the optical disc system provides an improvement of a performance and an operation in a random access or a program reproduction etc. based on non-contact reproduction, the improvement being hard to be realized in an analog storage/reproduction system.
Fig. 1 shows a schematic construction of an optical pick-up apparatus for reading data stored in a disc in an optical disc system.
Referring Fig. 1 , digital information is recorded in a disc 11 along a track (not shown), and laser beam focused by an object lens is irradiated onto a signal face of the disc 1 1 A focusing actuator coil 13 drives the object lens 12 so that the signal face of the disc 11 is positioned at the focal point of the laser beam, and a tracking actuator coil 14 drives the object lens 12 so that the laser beam using for an optical pick-up can be traced along by the track of the disc 11 Meanwhile, to position the signal face of the disc 11 at the focal point of the laser beam exactly, it is needed to maintain consistently an relativ e distance between the signal face of the disc 11 and the object lens 12. and for this, a focusing servo is generally executed and a tracking servo is performed for the laser beam used for optical pick-up to be exactly traced along the track Fig 2 indicates a circuit construction of a servo apparatus for detecting a conventional focusing error
In Fig 2, a focusing error signal is provided to a phase compensating part 21 to compensate a phase thereof, and then, is sent to a dm ing part 22 The driving part 22 drives a focusing actuator coil 23 in response to the focusing error signal compensated in phase As the focusing actuator coil 23 is driven, the object lens 12 of the optical pick-up apparatus shown in Fig 1 is adjusted and the signal face of the disc 11 is positioned at the focal point of the laser beam
At this time, phase compensating part 21 is to adjust the amount of the variation of the object lens 12 corresponding to the focusing error signal through changing of the phase of the focusing error signal That is, the phase is delayed for a specific focusing error signal, the object lens 12 insensibly react thereto while, when the phase is advanced, the object lens 12 sensibly react thereto Thus the sensibility of the phase compensating part 21 is properly determined and set such that a reaction of the object lens 12 for the focusing error signal ma> be adequate Fig 3 depicts a circuit construction of a servo apparatus for detecting a conventional tracking error.
Referring to Fig. 3. a tracking error signal is transmitted to a phase compensating part to compensate a phase thereof, and then, the compensated signal is sent to a driving part. The driving part drives a tracking actuator coil in response to the tracking error signal compensated in the phase. As the tracking actuator coil is driven, the object lens is traced to an eccentricity of the disc.
When performing such a disc servo, in the case of reproducing a bad disc, the focusing error signal or the tracking error signal is suddenly changed, thereby resulting in prohibition of an adequate focusing or tracking operation. Because of a fixed sensibility of the phase compensating part 21. 31. when the frequency of the focusing error signal or the tracking error signal is increased suddenly, the reaction of the object lens is rapidly changed, and a focusing servo or a tracking servo is not operated in proper, therefore, the focal point is deviated from the track or lost. In the servo apparatus for detecting the tracking error, however, a problem arise that not only the bad disc, but also a particle including dust and a scratch on the disc or a fine vibration by an external cause are regarded as a bad disc to thus narrow the bandwidth of the servo and limit the gain of the servo.
SUMMARY OF THE INVENTION
Accordingly, the purpose of the present invention is to provide a servo apparatus for detecting a tracking error in an optical disc system, which is capable of settling the above-mentioned problems.
Another purpose of the present invention is to provide a servo apparatus for detecting a tracking error in an optical disc system, in which an influence caused by a scratch or particle on the disc surface or a fine vibration by an external cause can be minimized.
To achieve these and other advantage, and in accordance with the purpose of the present invention, the servo apparatus for detecting a tracking error in an optical disc system is characterized by: at least two servo error detecting parts for outputting a servo error signal to determine whether or not there is a scratch or a particle on the surface of the disc, or a vibration of the optical disc by an external cause: a comparing part for recognizing the magnitude of the servo signals generated from said at least two servo error detecting parts and generating a signal representative of whether or not there is a scratch or a particle on the surface of the optical disc, or an occurrence of the vibration of the optical disc by an external cause; and a controlling part for minimizing a system error caused by the scratch or the particle of the optical disc surface and the vibration in response to a signal outputted from the comparing part.
BRIEF DESCRIPTION OF THE ATTACHED DRAWINGS
The invention will be better understood and its numerous objects and advantages will become more apparent to those skilled in the art by reference to the following drawings, in conjunction with the accompan ing specification, in which: Fig. 1 shows a schematic structure diagram of an optical pick-up apparatus for reading data stored in a disc,
Fig. 2 depicts a block diagram showing a servo apparatus for detecting a focusing error,
Fig. 3 depicts a block diagram showing a ser\ o apparatus for detecting a tracking error. Fig. 4 depicts a block diagram showing a servo apparatus for detecting a tracking error in an optical disc system in accordance with the preferred embodiment of the present invention,
Fig. 5 shows an output waveform diagram of the servo apparatus shown in Fig. 4, in the case of a scratch or particle on a disc surface.
Fig. 6 shows an output waveform diagram of the servo apparatus in Fig. 4, in the case of a vibration of a disc.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT Reference will now be made in detail to the preferred embodiment of the present invention, examples of which are illustrated in the accompanying drawings.
Fig. 4 shows a servo apparatus for detecting a tracking error in an optical disc system in the preferred embodiment of the invention. In Fig. 4, each of error signals 1, 2 is measured by a first servo error detecting part 100 and a second error detecting part 102 using a laser beam etc. and the measured signals 1 , 2 are inputted to a comparing part 104. Herewith, the number of the servo detecting part for outputting error signals can be reduced or increased according to the number of the laser beam irradiated, and in the embodiment, the number of the servo detecting part is not limited to two, rather increased two or more.
The comparing part 104 measures the magnitude of the error signals 1 , 2 and sends a signal representative of an defect caused by a disc surface, i.e.. a scratch or particle on the disc surface, or the vibration of the disc, to a controlling part 106. That is. if the following condition is satisfied: |Erl | or |Er2| > thl , the condition meaning that the magnitude of the respective error signals 1 , 2 is equal to or higher than a first threshold value thl , a signal 1 indicating an occurrence of a scratch or particle, or vibration on the disc surface is generated. While, if the following condition is satisfied:
|Erl - Er2| > th2 said condition meaning that a difference between the error signals 1 , 2 is equal to or higher than a second threshold value th2. a signal 2 indicating that the error signals 1. 2 measured by the first and second servo error detecting parts 100. 102 are equal to or higher than the second threshold value th2 is generated.
The signals 1 , 2 are inputted to the controlling part 106. and in the controlling part, it is recognized as a scratch or particle existing on the disc surface when both of the signals 1 , 2 are in active state, thereby a switch SW is cut off. In case only the signal 1 is in active, the switch is opened and the gain of a gain/compensating part 112 becomes large to make the servo apparatus have a strong characteristic against the vibration. A delaying part 108 delays the error signal 1 so as not to have little influence upon the servo apparatus due to a scratch or particle.
Fig. 5 shows output waveform from the servo apparatus shown in Fig. 4, in the case of a scratch or particle existing on the disc surface, and Fig. 6 depicts output waveform obtained in the case of a vibration.
Referring to Fig. 5, in case there exists a scratch or particle on the disc surface, the error signal 1 (waveform a) and the error signal 2(waveform b) are outputted from the first and second servo error detecting parts 100. 102 at a constant time interval. Then, the error signal 1 is delayed and outputted (waveform c) through the delaying part 108. In case the disc surface has a scratch or particle, the switch is cut off to thus generate waveform d and a subtracting part 110 outputs waveform e.
In Fig. 6. in the case of a vibration by an external cause, the error signal 1 , 2(waveform a-1 and b-1 ) are outputted from the first and second servo error detecting parts 100. 102 at the same time. When the vibration is occurred at the disc. a gain is increased to make the servo apparatus have a strong characteristic against the vibration as shown in waveform c-1.
According to the present invention as described above, the servo apparatus for detecting the tracking error comprises at least two servo error detecting parts for generating a servo error signal in order to determine whether there is a scratch or particle on the surface of the optical disc, or a vibration due to the external cause, in which the servo error detecting part uses a laser beam. As such, by comparing a number of the servo error signals outputted from at least the two or more servo error detecting parts and determining whether it is a disregardable scratch or particle, the possibility of an error in the servo apparatus can be minimized. In addition, in the case of a vibration of the disc by an external cause, a servo apparatus strong against a shock can be realized.
Although a preferred embodiment of the apparatus of the present invention has been illustrated in the accompanying Drawings and described in the foregoing Detailed Description, it will be understood that the invention is not limited to the embodiment disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the sprit of the invention as set forth and defined by the following claims.

Claims

What is claimed is
1. A servo apparatus for detecting a tracking error in an optical disc system, comprising: at least two servo error detecting parts for outputting a servo error signal to determine whether there is a scratch or particle on the surface of an optical disc, or a vibration by an external cause, in reproducing data stored in the optical disc; a comparing part for recognizing the magnitude of the servo signals generated from the at least two servo error detecting parts and generating a signal representative of whether there exists the scratch or particle on the surface of the optical disc, or the vibration of the disc by the external cause; and a controlling part for minimizing a systematic error caused by the scratch or particle, or the vibration in response to the signal outputted from the comparing part.
2. The servo apparatus of claim 1. further comprising a delaying part for delaying the servo error signal recognizing the scratch or particle so as not to have an influence upon the servo apparatus, in case there exists the scratch or particle on the optical disc.
3. The servo apparatus of claim 1 , further comprising a gain/compensating part for increasing a gain so as to make the servo apparatus have a strong characteristic against a vibration, in case the absolute value of each of the servo error signals outputted from the at least two servo error detecting parts is equal to or higher than a predetermined value.
PCT/KR2000/000611 2000-03-09 2000-06-12 Recovery from tracking errors on optical disks WO2001067444A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU2000251131A AU2000251131A1 (en) 2000-03-09 2000-06-12 Recovery from tracking errors on optical disks

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
KR10-2000-0011788A KR100371592B1 (en) 2000-03-09 2000-03-09 servo apparatus for detecting tracking error in optical disk
KR2000/11788 2000-03-09

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AU (1) AU2000251131A1 (en)
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Cited By (1)

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WO2006038138A1 (en) * 2004-10-05 2006-04-13 Koninklijke Philips Electronics N.V. Recovery of lost track focusing on an optical disc

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KR100408396B1 (en) * 2001-02-05 2003-12-06 삼성전자주식회사 Method for detecting disc crack and speed control method in the disc drive therefor
KR100964686B1 (en) * 2003-11-14 2010-06-21 엘지전자 주식회사 Method for testing Anti-Contamination of Disk Surface
KR100555553B1 (en) 2004-02-05 2006-03-03 삼성전자주식회사 Apparatus and method for compensating defect of optical disc
KR100964704B1 (en) * 2009-02-25 2010-06-21 엘지전자 주식회사 Method for testing Anti-Contamination of Disk Surface

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Publication number Priority date Publication date Assignee Title
WO2006038138A1 (en) * 2004-10-05 2006-04-13 Koninklijke Philips Electronics N.V. Recovery of lost track focusing on an optical disc

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KR100371592B1 (en) 2003-02-14
AU2000251131A1 (en) 2001-09-17
KR20010087922A (en) 2001-09-26
KR200192776Y1 (en) 2000-08-16

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